No lift pump?!!

[Alastairdent]

Finally got our engine going, after about 10 attempts in the last 2 weeks. The engine on the sailing barge hasn't been run since we sailed her over from the nederlands.
I couldn't figure out what was stopping it from starting. Air filter ok, starter batteries charged, spinning over, fuel bled through new filters . . .

Eventually, I remembered the sign behind the oil heater. This says (rough translation) "Turn off the stove before starting the engine.". So I did, and the engine started . . .

This is odd, because although they are both fed from the same header/day tank, they don't share pipework. The tank is about 3ft above the engine. The only thing I can think of is that the lift pump on the engine isn't working, and it relies on the 'head' of diesel. When the stove is on, the slight fuel flow to the stove is enough to create a slight vacuum in the day tank - the air breather is small - and slow/prevent enough fuel from getting to the engine.

Any of you engine experts out there agree? If the engine lift pump is working, I wouldn't have thought that the slight flow of fuel to the drip-burner diesel stove could possibly stop the fuel from getting through to the engine.

 

[Evadne]

I'm not sure I'd call myself an expert, but it sounds possible. Is there a cap on the day tank you can remove, to test your theory? The engine should start with the stove on and the cap off if it's a breathing problem.

 

[Alastairdent]

Nope, no cap I can remove.

 

[boatmike]

Sounds very weird! A thought. When you say they don't share the same pipework, this can only truly be so if there are two outlets from the tank. If there are gawd knows what the problem is! However if it is ONE outlet branching into two pipes at a tee piece for instance, the engine would suck air back up through the cooker pipe before diesel from the header tank.....???????

 

[Alastairdent]

Two outlets.

It is wierd. The day tank is diy (in a shipyard, by the steelworker who owned the boat).

I want to do away with it and take the fuel from the main tank.

However, if the lift pump is not functioning, that's a non-starter (pls excuse the pun).

Any DAF experts here who can help me test the lift pump?

 

[boatmike]

There may be a clue in the fact that it does not have a filler cap. Does it have a pressurised single line feed from the main tank or is there a return / overflow / line back to the main tank?
I assume that the main fuel tank is below the header tank and has a pump feeding the header tank. What tells that pump to stop pumping?
Could you describe the system more fully?
There are at least three ways to plumb in a header tank.
1. Single line feed to a closed tank which is really just a manifold to tap off.
( These need a bleed valve in the top to get the air out.)
2. Single line feed with return to main tank where the feed comes in half way up the tank and when the level reaches the pipe the pressure sensitive pump stops.
(This should have an overflow to main tank above the inlet)
3. Single line feed to the tank with a ball cock float valve and overflow.

If it is the first option with a sealed tank it will actually do just the same as a gravity tank with a common pipe as I said before. If it's easier to suck air up the cooker pipe than fuel from the main tank you will get an airlock and no fuel will flow. To run two feeds from one tank the top must be open to atmosphere even if only through a return line to the tank. Kapish?

 

[Twister_Ken]

I'm tempted to say don't mess with it. Boats are idiosyncratic. If the engine wants the heater off, that's just the way it is.

 

[Alastairdent]

The header/day tank is filled by a manual pump.

The top of the day tank has a fuel hose running back to the main tank, this is the overflow.

The main tank has a breather pipe to a deck fitting.

Originally, there wasn't a breather pipe, and the 'overflow' on the day tank was just a hole on the top - so if you pumped too much fuel into it, the fuel just overflowed down the tank into the bilge. The engine return line goes to the day tank.

There wasn't a filter between the tank and the engine, I added a fuel filter.

The last big trip we did, we put a 1000l temporary tank on deck, and I bypassed all this crap, using temporary copper fuel pipe from the deck tank to the engine.

It is a mess currently, I'd quite like to ditch it all. But if the lift pump ain't working, then I need to start with that, methinks.

 

[brianrunyard]

What sort of breather has the day tank got?

 

[Alastairdent]

The only breather is the fuel overflow pipe, lead back to the top of the main tank. The main tank has a proper deck breather.

 

[boatmike]

Obviously this "header" tank is quite big. Usually header tanks are relatively small. It is acting as a gravity feed tank to the engine and heater / cooker whatever and frankly if you took the connections to the main tank away it would be the same as any other diesel tank apart from the fact that it has gravity feed which is a good thing. I am sure your engine will have a delivery pump and think this is a red herring. Why the damn thing won't start unless you turn the other feed off I don't know. Are you sure this wasn't a coincidence? What happens if you try again with the other feed on? What happens if you turn the feed on while the engine is running? Either there is something you have missed, or this is just an intermittent engine fault that you are assuming is associated with the other feed......But then why the sign in the first place?????? /forums/images/graemlins/confused.gif

 

[Alastairdent]

I'd like to think you are right . . . .

I guess the best thing is to run the engine again, and turn on the stopcock to the diesel heater, like you suggest. If the engine cuts out, then I'm not sure what to think, apart from suspecting the lift pump.

I could also make a temp connection to a jerrycan - if the engine lifts the diesel from the jerrycan, obviously it has a working pump.

 

[boatbuilder]

What make and model is the engine?

 

[VicS]

[ QUOTE ]
The only breather is the fuel overflow pipe, lead back to the top of the main tank

[/ QUOTE ] This is part of your problem, I suspect. Unless the overflow pipe is a largish diameter and runs directly down to the main tank with no horizontal sections it is going to retain some fuel and the "head of fuel" retained in that pipe is going to lead a small reduction in pressure in the head tank. Not much perhaps but just enough to prevent a good flow of fuel to the engine when the stove is working.

Test my theory by disconnecting the overflow pipe from the head tank and see if that solves the problem.

Even if that is the problem, like you, I would have expected the engine lift pump to have drawn fuel if it was working correctly but with an unobstucted feed from an elevated tank there should be no need for a lift pump. No need to lift the fuel if it isalready above you.

Ultimately several solutions. <ul type="square"> [*]Separate the overflow and vent on the head tank, a tee piece on the head tank will do that adequately, and forget the lift pump [*]Overhaul the lift pump and leave the tank over flow as it , but it would still be better to separate the overflow and vent [*]Use the head tank for the stove and draw the engine fuel directly from the main tank. That will need the lift pump to be in working order [/list]


Just re-read some of what you have said.. The filter between the tank and the engine may not be helping but if it is adequately sized it should be ok.

 

[Alastairdent]

The engine is a DAF 575, 120hp with the turbo.

Whatever I do has to comply with BSS regs, which does complicate things a little. There aren't any horizontal sections on the overflow pipe (BSS regs again).

I'd rather switch the engine onto the main tank, the header only holds enough fuel for 5 hours. As you say, that requires a working lift pump.

Thanks for everyone's help, I think I'm going to have to bite the bullet and test/strip/replace the lift pump.

 

[boatmike]

Keep us posted as to how you go on! I for one am interested to see what the problem turns out to be. As far as the overflow is concerned, as long as the bottom end of it is above the level of the fuel in the main tank and it's diameter is no less than that of the main feed to the engine from the header tank it can't be the problem. I can't remember where the lift/delivery pump is on the DAF but it's got to be at the end of the fuel line (doh!) so easy to locate. It may in fact have a manual priming lever on the side which may enable you to test it but personally I am pretty sure it will be OK. If it is not working properly you should be able to get a recon kit and diaphragm for it from any DAF agent. They are usually not too bad to get spares for. I think your problem is very likely elsewhere but will be interested to know when you find out.